Question

Which of the following compounds will show metamerism? (a) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}\) (b) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2} \mathrm{H}_{5}\) (d) \(\mathrm{C}_{2} \overrightarrow{\mathrm{H}}_{5}-\mathrm{S}-\mathrm{C}_{2} \mathrm{H}_{5}\)

Short answer

Compounds (a) and (c) show metamerism.

Step-by-step solution

Understanding Metamerism

Metamerism is a type of isomerism where compounds have the same molecular formula but different alkyl groups on either side of a functional group. This usually occurs in compounds like ethers, thioethers, and sometimes ketones.

Analyze Option (a): Ether

The compound \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}\) is an ether because it contains an oxygen atom between two alkyl groups. To check for metamerism, the compound must be rearrangeable to form another ether with different alkyl groups. Upon rearrangement, it can form another compound, \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{O}-\mathrm{CH}_{3}\). Hence, it shows metamerism.

Analyze Option (b): Simple Ether

The compound \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{3}\) is also an ether, but it has identical methyl groups on each side. Because there are no different alkyl groups that can be rearranged to form another structure, it does not show metamerism.

Analyze Option (c): Ketone

The compound \(\mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2} \mathrm{H}_{5}\) is a ketone. Ketones can sometimes exhibit metamerism. By swapping the methyl and ethyl groups around the ketone group, we get \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{CO}-\mathrm{CH}_{3}\). Hence, it does show metamerism.

Analyze Option (d): Thioether

The compound \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{S}-\mathrm{C}_{2} \mathrm{H}_{5}\) is a thioether with identical ethyl groups on both sides of the sulfur atom. As no different rearrangement of alkyl groups is possible, it does not show metamerism.

Conclusion

The compounds that show metamerism are options (a) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}\) and (c) \(\mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2} \mathrm{H}_{5}\).

Key concepts

Isomerism

Isomerism is an intriguing phenomenon in chemistry where molecules share the same molecular formula but have different structures or spatial arrangements. This difference in structure can lead to varied chemical and physical properties.
There are several types of isomerism, including:

• Structural Isomerism: Variations in the connectivity of atoms.
• Stereoisomerism: Variations in the spatial arrangement of atoms.
  • Cis-trans isomerism
  • Optical isomerism

Metamerism is a specific type of structural isomerism where the isomers differ in the alkyl groups attached to a central functional group, such as an ether (\( ext{R}- ext{O}- ext{R}' \)). This unique rearrangement of alkyl chains can markedly alter a compound's behavior in chemical reactions and its dissolution properties.

Functional Groups

Functional groups are specific clusters of atoms within molecules that govern the molecule's chemical properties and reactions. They are the reactive part of the molecule and are responsible for the characteristic behavior of different classes of compounds.
Key functional groups include:

• Hydroxyl groups (-OH) in alcohols
• Carbonyl groups (C=O) in ketones and aldehydes
• Carboxyl groups (-COOH) in carboxylic acids
• Amino groups (-NH\(_2\)) in amines
• Ether linkages (R-O-R')
• Thioether linkages (R-S-R')

These groups help in identifying how molecules interact, react, and function. For instance, the presence of an iodine group can increase molecular weight and affect the molecule's solubility and boiling points.

Organic Chemistry

Organic chemistry is the branch of chemistry that deals with carbon-based compounds, which can form a vast array of structures due to the ability of carbon atoms to form strong covalent bonds with themselves and other elements such as hydrogen, oxygen, and nitrogen.
Key aspects of organic chemistry include:

• Structural formulas
• Understanding isomers
• Identifying functional groups
• Studying reaction mechanisms
• Synthesis and analysis of organic compounds

Organic chemistry is essential for understanding the molecular foundations of life, as it underpins biochemistry, pharmaceuticals, plastics, fuels, and dyes. It is the study of molecules that make up living organisms and synthetic substances used in everyday life.

Ethers

Ethers are organic compounds characterized by an oxygen atom connected to two alkyl or aryl groups, denoted as R-O-R'. Ethers are relatively non-reactive, which makes them excellent solvents for organic reactions.
Some important points about ethers include:

• They have polar bonds because of the oxygen atom, but the molecules themselves are non-polar.
• Ethers can form hydrogen bonds through their oxygen atom but cannot donate hydrogen for hydrogen bonding.
• They have boiling points similar to alkanes of comparable molecular weights.
• Metamerism in ethers arises when the alkyl groups (R and R') are rearranged to form different ether isomers, such as in the compound \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2}\mathrm{H}_{5} \).

Ethers have applications ranging from anesthetics to solvents in laboratory and industrial settings.

Thioethers

Thioethers are similar to ethers but with a sulfur atom replacing the oxygen atom. They have the general formula R-S-R'. The presence of sulfur imparts distinctive chemical properties different from those of ethers.
Key characteristics of thioethers include:

• Sulfur is less electronegative than oxygen, which affects the bond polarity and thus reactivity.
• Thioethers have higher boiling points than ethers due to stronger van der Waals forces.
• They can form different types of isomers, just like their oxygen-containing counterparts.
• The sulfur atom can confer distinctive smells, which explain their presence in certain biological and synthetic materials.

In nature, thioethers occur in the structure of biomolecules such as methionine, an essential amino acid. Additionally, they are used in certain types of chemical syntheses in industrial settings.

Ketones

Ketones are a group of organic compounds characterized by the presence of a carbonyl group (C=O) bonded to two carbon atoms. They follow the general structure R(CO)R'.
Notable aspects of ketones include:

• The carbonyl group is a significant site of reactivity, particularly in nucleophilic addition reactions.
• Ketones are typically less reactive than aldehydes due to steric hindrance and electronic effects.
• They have relatively high boiling points compared to nonpolar compounds of similar molecular weight, due to dipole-dipole interactions.
• Metamerism in ketones occurs when the alkyl groups (R and R') around the carbonyl group are rearranged into different positions, as demonstrated in \( \mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2}\mathrm{H}_{5} \).

Common ketones include acetone, used as an industrial solvent, and natural metabolic compounds like fructose in sugar metabolism. Ketones are pivotal in both synthetic organic chemistry and biochemistry.